Method of concentrating radium bearing ores



May 7, E940. H, FLECK 2,199,697

METHOD 0F GONCENTRATING RADIUM BEARING ORES Filed Jan. 3, 1938 Patented May 7, 1940 UNIT STATES maar PATENT GFFECE METHOD F CONCENTRATING RADIUM BEARING ORES deceased Application Janar'y s, 193s, serial No. 183,115

1 Claim.

This invention relates to a process for concentrating radium bearing ores, more particularly to a method for freeing radium from the refractory, siliceous and aluminous gangue and 5 impurities contained in low grade radium ores and concentrates.

Heretofore, the treatment of the low grade radium ores, which are relatively abundant in nature, has been an exceedingly costly and wastel0 ful proceeding due to the sulphate radical, gypsum and other dimcult impurities. Most prior methods have endeavored to avoid the detrimental constituents by a careful selection of the ore by cobbing or other means so as to retain for treatment only the ores or portions of the ores which have a minimum of the interfering constituents. This careful selection necessitates the discarding of the major portions of the radium bearing oresand the loss of large amounts oi' valuable radium carried therein.

Other processes endeavor to avoid the above selection losses by refining out the objectionable sulphate radical and the gypsum by long, tedious, costly and wasteful multi-step processes which are often highly destructive of apparatus and productive of noxious gases, and which are in most cases a menace to the health of the workers.

The principal object of this invention is to DIOVde a simple and ecient process which will overcome the above objections to present processes and which will enable comparatively low grade ore or concentrates to be treated at a profit.

One of the diiculties encountered in the concentration of radium arises from the fact that the radium and radium bearing materials react similarly to the useless sand and gangue when subjected to acid treatment, that is, they all go down together with the tailings. Another object of this invention is to provide a method whereby the undesirable portions of the tailings or gangue will become acid soluble while the radium materials will remain insoluble so that the two can be quickly and easily separated by a simple acid bath.

Other objects and advantages reside in the improved process and in the means for carrying out the process. These will become more apparent from. the following detailed description thereof in which reference is had to the accompanying drawing which illustrates a typical flow chart of the process.

While the process is particularly designed for the treatment of Carnotite ore, it is of course not limited thereto as it will be found valuable for the recovery of radium, or the salts or compounds of radium, from pitchblende and other minerals carrying radium values and from radium slimes or other silicious, aluminous admixtures containing radium or radium compounds.

Carnotite is a mineral containing uranium, vanadium, radium and a well dened amount of barium. The mineral is usually found impregnating or encrusting sandstone and argillaceous shales, with lime as a binder between the sand grains. All combine to produce a very low grade original ore.

Briey the method comprises (1) mechanically concentrating the ore to eliminate a major portion of the sandstone and shale; (2) dissolving oi the vanadium, uranium and other metals with acid and settling out the sands while holding the insoluble radium bearing slimes in suspension; (3) ltering out the slimes; (4) digesting the slimes with heat in a Water solution of caustic to change the worthless silicious portion of the slimes from an acid insoluble state to a Water insoluble and acid soluble state while retaining the radium-barium salts acid insoluble; (5) thence dissolving out the worthless material from the slimes with acid to leave a rich radiumbarium concentrate.

As an auxiliary to the main method a simple and eicient method (4a) is provided for removing the silica and recovering and purifying the used caustic for reuse in the alteration step of the main process.

The principal contribution of this invention is step (4) wherein the silicious matter in the slime which heretofore has been so diflicult to handle is easily and rapidly changed to a state which allows it to be dissolved from the Valuable radium bearing concentrate in a single, simple operation.

The process can best be understood by following through a typical batch of ore, reference being had to the flow diagram on the accompanying drawing.

Step #1 The ore is first prepared by a roughing treatment to obtain a rough concentrate richer in radium than the original ore. This may be done by crushing and grinding to a neness not less than the size of the sand grain of the ore or more precisely to a state of comminution as exactly as possible to expose the radium bearing mineral particles, (usually 20 to 30 mesh).

Step #2 The above comminuted ore is now fed to acid treaters, preferably conical bottomed discharge tanks provided with suitable agitators to which a hot aqueous solution of' sulphuric acid (approx. 20% solution) is fed. In the acid treatment the uranium, Vanadium, iron, and a portion vof the aluminum and lime present go into sulphate solution.

The yheavy barren'sands gravitate to the bottom and are drawn off to waste, 'thelighter sand particles remain in suspension as a iine silicious slime.

The radium remains withthel iinersparticles of' the ore in the form of the insoluble sulphate. The latter particles are kept in suspension in the solution by the agitators andareldrawn ''i'with the sulphate solution to a suitable settling tank.

Step #3 The clear liquor from the settling tank is .-now drawn off Vfor the recovery of the valuable constituents inthe solution.

A method of treating/'the latter Asolution vis outlined in4 applicants copending application Serial No. 180,403 and forms no partof thepresent invention. f

It is to the settled slimes that this 'invention is particularly directed. These slimes 'consist ofa soft mud or slime of clay; shale, and gypsum in more or less colloidal state, containing radium, the amount depending -upon the percentage of uraniumin the ore and the nature and amount ofslime forming ingredients. An ore containing one-half of one percent of uranium` oxide (equivalent-to one and three-tenths milligrams of radium metal'per ton of ore) will yieldla slime Vwhich mayl contain nearly all of the original radium varying from six to `twelve milligrams perton.

The slimes will be hereinafter referred toas radium slimes. Itis desired to be understood however that the following steps are applicable to the treatment of any radium bearing mate- I Vrial and are -not limited to the treatment of vthe specific acid radium slimes above described.

Step#4 The radium slimes are now placedin4 suitable caustic pots with an aqueous solution `of caustic soda and heated sufciently to cause active ebulition or digestion (below 200 C.). It has been'found that other caustic hydroxides may be used in place vof caustic soda.

The latter,v however, is the preferred caustic, and the preferred proportion lis one part dry slime to two parts 80% aqueous caustic soda solution. A lower strength may be used if desired the only effect being upon the time element.

The 80% caustic soda solution possesses the quality of low temperature liquidizing (below 200 C.) "At this temperature the solution can be pumpedl or diluted and pumped or otherwiseconvenientlyhandled.

poured on the slimes or the slimesaddedto the solution, etc.

Reaction begins immediately below 200 C. in the caustic pots and is completed in a few hours. The slimeswll be disintegrated-aportion of the l and allowed to settle.

.the sulphate radical present, however, the vall0 'uable radium-barium residue remain insoluble sin acid.

These new properties of the radium slimes which were attained by a single, simple, economicalstep'make itpossible to now readily separate l5 the worthlessmaterial from the valuable radiumbarium residue.

The'zdigested z mass, while still hot, is now brought to a dilution of approximately twenty perr cent of the original caustic (dry weight) 20 ,TheNaOI-Ii liquor with sodium. silicate is decantediand refined 'for' the removal of the latter as described in step 4a, below. The residue may be further-washedwor iilter pressedv toV produce a highly concentrated, chem- 1. 25 ically altered slime cake.

'Step #5 The concentratedl slimecake'is now admixed with dilute acid preferably, `but notnecessarilystao hydrochloric acid. The solutionis kept cold and the, now very small volume of, radium-barium sulphate residue, containing` substantially. all of the radium, ywill settle rapidly. .The l'acidirled supernatant liquor is quicklyruno'towaste135 before' there iis an appreciable' formation-'of in.w

soluble silicio acid.

The radium-.barium sulphate residue (a concentration ofv from '75v to 1GO-:times .that;of the original ore) isnow ready for the `cryst'allizing.140 stage to produce salts 'of radium: of thigh purity. The iinal crystallizing can be accomplished by the methodsy known to thosevskilled in' the art and'forms no part ofthe 4present invention.

step 4a 145 The caustic liquor from' step 4 containing sodium silicate, sodium aluminate and otherfimvpuritiesfis now treated to recover the caustic for reuse in step 4. This is very economically` andijs50 veliciently done by adding hydrate of lime in a `suitable settling tank or cone.

l This lime yreacts quantitatively to precipitate' calcium silicate and calcium `aluminate which are settled andlor iiltered off to waste. The remaining solutiong/55 (approx. v 20%'NaOI-I) is evaporated back-to a concentration of 'i0-80%` for reuse inthe caustic pots. hArecovery of- 'of caustic' can bev made ifl all caustic wash-'waters and solutions are returned to step 4a. 60

While hydrate of lime is the-most economical and lconvenient reagent for use in purifying the caustic solution of silica and aluminum, common `burned lime or caustic'lime may' beused with lequal results.

65 mile the process has been described as using sodium hydroxide or 'soda lye yas a caustic, it

could be carried out equally well with potash lye 'at somewhat greater expense. 'The aqueous '-liiu'id solution and moreeconomical in cost.

IfY desired,` the ground ore of step '#1 may be:A 75

treated by any of the Well known mechanical concentration methods to obtain a richer concentrate before the acid step #2. The preferred procedure, however, is to feed the natural ore direct to the acid treatment to immediately free and place the radium slimes in suspension so that they may be removed from the barren sand by elutriation in a single simple step.

Eighty per cent caustic solution is the most favorable caustic concentration in the caustic pots. However, the process is by no means limited to an 80% solution since even a 50% concentration Will give perfect results over a longer time interval.

A higher concentration than an 80% solution is neither necessary nor desirable to accomplish the alteration to the acidV soluble form. Extremely high concentrations would entirely destroy the composition of, and dissolve, the 'slimes which of course is not the purpose of the caustic step.

While the improved process has been described in some detail in order that those skilled in the art will be enabled to place it in practise after the expiration of any patent or patents which may be issued thereon, it is desired to be understood that the invention is not limited to the precise procedure described nor is it dependent upon the accuracy of any theories Which may have been advanced herein. On the contrary, the invention is not to be regarded as limited in any Way except in so far as such limitations are contained within the scope of the accompanying claims in which it is intended to claim the invention as broadly as possible in View of the prior art.

Having thus described the invention, what is claimed and desired secured by Letters Patent is:

A method of separating siliceous matter from radium-barium sulfate slimes, comprising: heating said slimes in a concentrated aqueous caustic soda solution consisting of not over 80% caustic soda to a temperature of not over 200 C. which Will effect the solution of at least a portion of the silica in the siliceous material present, diluting said solution and separating the same from the residue, treating said residue While maintaining it cold with dilute acid to dissolve impurities in the residue While retaining the radium in said residues and separating said acid from the residue so rapidly that no siliceous precipitate separates.

HERMAN FLECK. 

